The whistleblower, who has 32 years of experience working inside polling stations, told the Nolan Show that many people coming to vote at a Downpatrick polling station were erroneously not on the electoral register.
He said: “People were coming in with their correct ID and their polling card with all the information on it who obviously should have been on the register but were left out.
“People’s families were coming in, four of them were coming in and three of them were on the register and the fourth one might not be.
“They all got the poll card delivered at the same time obviously, (they were saying) I have got my poll card, I have got my ID and I have been left off the register now. It was happening so often.
“I can see it happening once where an error has been made when you are not on the register and you can be offered a tendered ballot paper, but this is happening so often, rightly or wrongly I made the decision to give them a vote.”
The whistleblower said there was three ballot boxes in his polling station, and each one had the same problem.
“It was happening on average once an hour were people we coming in without their cards, or with their cards and not on the register,” he added.
The polling station manager said he has never experienced problems like this in the past.
“I also had a young girl coming in who was honest enough to admit to it, she came in with two polling cards one under her first name and surname and another with her first name, middle name and surname and she told me they were both her cards,” he said.
“She appeared on the register twice, so in theory she could have come in under one and voted and come back awhile later and voted again.”
The whistleblower described the situation as a “shambles and an embarrassment” and called for an investigation into the matter by the Electoral Office.
“They (Electoral Office) must know themselves it is something that it needs to look into. I don’t know how the candidates in the marginal seats think, who lost by 50 votes. If you lost by a small amount, are you thinking I could have made those votes up somewhere else?”
The Nolan Show has also revealed that the Electoral Office told a voter in the Fermanagh and South Tyrone constituency that the deadline to submit information to be put on the register was December 3, when in fact it was December 4.
It raises questions about the outcome of the vote in seats with marginal majorities, including Fermanagh and South Tyrone, which Sinn Fein’s Michelle Gildernew won with a majority of just 57 votes over the UUP’s Tom Elliot.
Last week a 23-year-old whistleblower, who was sacked from his role within the Electoral Office, made a number of allegations about how voter registrations were handled in the lead up to the December 12 election.
The whistleblower told the BBC that:
Valid applications for postal votes were rejected by the Electoral Office due to errors
Some applications to register to vote were only processed 24 hours before the deadline to submit additional evidence, such as proof of identity or address
Potential voters were given an incorrect date for the deadline to submit additional evidence to support their application
Helpline operators on one occasion were asked to share one Nokia phone to field calls from all over Northern Ireland
Ulster Unionist Party Steve Aiken, speaking on the Nolan Show, said the situation was “very worrying” and said his party was taking legal advice on the matter.
“As an MLA, and listening to our MLA group and talking to other political parties, these issues around polling cards, people turning up at polling stations and not being on electoral register, I am picking up things all across NI about this,” he said.
“There are real issues that need to be addressed here and we need to have a thorough investigation into what is happening at the Electoral Office.”
Candidates only have 21 working days to challenge an election result.
The Electoral Office was not available for comment but in a previous statement promised to investigate the claims.
With many thanks to the: Belfast Telegraph and Mark Edwards for original story